The present invention relates to a seal assembly for use in an injection molding process and; more particularly, to a seal assembly for use in a mold for making encapsulated window structures.
Initially, fixed window assemblies for vehicles were comprised of a plurality of elements including adhesive sealants applied around the marginal edges of a glass sheet, suitable mechanical fasteners such as metal clips, and exterior decorative trim strips disposed to cover the junction between the marginal edges of the glass sheet and the adjacent portions of the vehicle frame. Such window structures were costly, especially from a labor standpoint, since it was necessary to assemble the individual elements along the vehicle assembly line.
Subsequently, in an endeavor to improve the above window structure, unitary window assemblies of the type illustrated in U.S. Pat. No. 4,072,340 were developed. These window assemblies included a sheet of glass, an adjacent frame, and a casing or gasket of molded material, such as polyvinylchloride, extending between the frame and the peripheral edge of the window to hold the sheet of glass and the frame together. Fasteners were provided at spaced locations along the frame such that the entire assembly could be guided into a location over the opening in a vehicle body as a unit. Other types of unitary window assemblies are disclosed in U. S. Pat. Nos. 3,759,004 and 4,364,595. While such unitary window structures greatly reduce the time required to mount the window assembly in an associated vehicle, such structures are relatively costly, since the individual components required to produce each window assembly generally must be manually assembled.
Recently, window assemblies have been formed by encapsulating at least a portion of the periphery of a sheet of glass with a gasket material. Typically, the gasket is formed by curing a polymeric gasket-forming material in situ on the glass sheet to encapsulate a predetermined portion of the marginal edge of the sheet. The gasket can be polyurethane and formed, for example, by a reaction injection molding process.
A mold structure which can be utilized to encapsulate a glass sheet with an integrally molded gasket is disclosed in U.S. Pat. No. 4,561,625 issued to W. R. Weaver and assigned to the assignee of the present invention. In this patent, the mold structure includes at least two mold sections having facing surfaces cooperating to define a chamber for receiving a glass sheet. A resilient seal means is positioned in at least one of the mold sections about at least a portion of the periphery of the chamber and functions to resiliently support the glass sheet within the chamber. Each mold section includes a metallic main body portion, and the seal means maintains at least the portion of the glass sheet located inwardly of the seal means in spaced-apart relationship with the metallic main body portions of the mold sections.
Also, in the Weaver patent, the seal means cooperates with predetermined portions of the glass sheet and the mold sections for defining a gasket forming cavity having a configuration corresponding to the gasket to be formed on the glass sheet. At least a portion of the facing surfaces of the mold sections disposed outwardly of the gasket forming cavity are in metal-to-metal contact with one another. This enables the amount the seal means is compressed and the dimensions of the gasket to be controlled.
The prior art seals are typically deformable, static silicone rubber or Teflon coated elastomeric seals. In order to accommodate differences in contour or edge profile which occur between individual glass sheets, these seals must be deformed sufficiently to fill "low spots" and prevent gaps between the glass and the seal which would cause excessive flash formation on the gasket being molded. This deformation causes very high pressure on the high spots, resulting in seal fatigue and leading to premature seal failure. In some instances, the excessive pressure may cause breakage of the glass sheet. In all cases excess pressure distorts the seal contour resulting in distorted molded gasket shapes.